Electronic appliances are increasingly being used for self-medication in medical electronics, with these appliances generally being worn by the user directly on the body and supplying the medicament liquid continuously or quasi-continuously, as appropriate for the therapeutic requirement. By way of example, computer-controlled insulin pumps are being used for the treatment of diabetes mellitus, allowing the patient to be supplied with an insulin level which corresponds to the physiological characteristics of a non-diabetic, to a good approximation.
In order to allow the therapeutic end to be achieved, a series of fundamental requirements must be satisfied. Under all circumstances, it is necessary to avoid the power supply to the medical appliance failing without this failure being evident.
Since the apparatus is subject to considerable mechanical forces during normal daily use and its individual parts have different moments of inertia, it is possible in the event of a corresponding force influence, for example as a result of a sudden movement by the user, for the battery to be disconnected from the contact spring for a brief moment, causing a brief interruption in the voltage. Such inadvertent and possibly unnoticed resetting of the apparatus can have serious consequences for the supply of the product, and patient safety.
Furthermore, it will be desirable to bridge relatively long failures of the power supply which can occur, for example, during replacement of the batteries, in order to avoid the need for monitored and time-consuming resetting of the insulin pump to a rest state.
Power supplies for insulin pumps are known from the prior art which allow more far-reaching so-called power management. Patent document EP 0168 472 discloses a fluid pump apparatus with a supporting energy source whose object is to allow the first power source to be supplied with sufficient energy, although the insulin pump functionality is greatly restricted in this operating mode. Power management systems are likewise known from the prior art which, when the energy source is identified as having been exhausted, change to an operating mode in which the insulin pump is stopped. The insulin pump therapy cannot be continued until a new battery has been inserted and the insulin pump has been set to the operating mode again, by the user.
The time at which the energy sources will become discharged can be predicated only imprecisely owing to the various influences acting on the stored rated energy of the energy source, for example storage conditions, temperature, age of the battery. If the energy cells for a patient become discharged during the night, the patient must be woken up from his sleep by requesting him to change the batteries. Even during the normal course of the day, it is desirable to have a certain emergency power reserve available, for example if a new energy source is not immediately available to the pump wearer.